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Tube Diagnosis

I am a bit limited in my experience with Tube quirks so looking for a bit of insight.

With no music playing I noticed a small amount of noise coming from the left channel of my system a couple weeks ago.

I isolated it to my preamp (Aesthetix Calypso - 12AX7 gain and a 6922 output in each channel) and then further to the left channel output tube. I did this by swapping the left and right output tubes and the noise moved with the tube.

I am running used tubes with a reasonably low but unknown amount of hours, all was silent until a couple weeks ago. Telefunken ECC803S for Gain and amperex PQ white 6922's for Output.

The 'noise' is a low level crackle that seems random. i.e. crackle crackle---silence for a random amount of seconds--crackle and so on. It is independent of volume and does not change if the tube is lightly tapped! The noise is low as I mentioned but can be heard during silent sections of music and is distracting enough for me to buy new tubes to get rid of it. The only other thing I have noticed is that the noise is a bit more pronounced when I first turn on the system, after it warms up things mellow but the noise does not go away.

I have experience with tube rush and what I would call microphonic noise - tube noise that increases with volume and responds to tapping of the tube. This is something different.

So, is this the sound of a Tube that is dying or just a tube that went noisy and will now stay that way?

Thanks
nikturner920

Showing 2 responses by larryi

larryi
3,722 posts
 
The first thing I would do is clean the pins on the tube and the socket. Poor contact sometimes causes that kind of noise.

Is it coming out equally from both channels or only one channel? If it is one channel, you can isolate the offending tube (if it is the tube) by swapping left and right tubes to see if the problem follows a particular tube.

I hope it is not the 803S. I run those in a phono stage and they are really big bucks these days.
larryi
3,722 posts
 
If you can find a vial of Caig Deoxit, that is a pretty good product for cleaning contacts, including tube pins and sockets. I like the super concentrated form of deoxit that is not in a spray can, but has a very thin needle like dispenser. A very small amount on a Q-tip that has been shaved down to fit between the pins works well. This gives a more heavy duty cleaning than the eraser, though I like that approach too.

For the tube socket, I use one of those specialty toothbrushes that are designed to go between the teeth. They look like they have only one fuzzy protrusion on a toothbrush handle.

Good luck on your noise fighting venture.
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